perl -le '$_ = "a"; print do { if( length ){ "A" } else{ "B" } };'

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A

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perl -le '$_ = "a"; print length ? "A" : "B" '

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Warning: Use of "length" without parentheses is ambiguous at -e line 1.
Use of ?PATTERN? without explicit operator is deprecated at -e line 1.
Search pattern not terminated or ternary operator parsed as search pattern at -e line 1.

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perl -le '$_ = "a"; print length . '' ? "A" : "B" '

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Use of ?PATTERN? without explicit operator is deprecated at -e line 1.
Search pattern not terminated or ternary operator parsed as search pattern at -e line 1.

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perl -le '$_ = "a"; print length + 0 ? "A" : "B" '

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Warning: Use of "length" without parentheses is ambiguous at -e line 1.
A